The invention rerales to an IC engine of the piston type comprising at least one engine inlet valve located between an inlet duct and each combustion chamber and a swing type check valve which is placed in the inlet duct upstream from the engine inlet valve, is adapted to shut against the direction of inlet flow and is engaged with an electromagnet in the shut setting, such check valve having an adjustable opening threshold with a time lag with respect to the start of inlet of the engine inlet valve.
An IC engine of this type is described in the German patent publication 3,737,828 A.
The swing type check valve constitutes a particularly simple, economic and reliable way of achieving an advantageous effect, more particularly at low engine speeds. The engine inlet valve opens while the check valve is still shut. Firstly the air present in the inlet chamber between the inlet valve and the check valve first expands into the engine cylinder. If the opening of the check valve is late enough there is a vacuum in the engine cylinder. The pressure differential upstream and downstream from the check valve leads to a correspondingly high speed, after the valve has opened, of the combustion air which then flows in. Towards the end of the piston stroke this flow speed is reduced so that there is a dynamic increase in pressure even prior to the shutting of the engine inlet valve. The backward flow of charge from the engine cylinder occasioned by this boosting of pressure may then be precluded by timely shutting of the check valve.
The swing type check valve may automatically open and shut independently of additional control or automatic control devices, in which respect however there is the possibility of performing an adjustment in a simple manner in order to affect the time lag of the point in time of the opening of the check valve.
Once the opening threshold, which has previously been set, is reached, the check valve is able to open under the effect of the vacuum on the engine side. When the pressure on the engine side has increased to such an extent that the check valve is likely to be subjected to return flow of the charge out of the engine cylinder, it will automatically shut.
The said German patent publication 3,737,828 has already provided a suggestion to time the check valve opening so as to be related to angular position of the crank shaft, as for instance by a latching device released in a manner dependent on the engine crank shaft angle. On the other hHand there has also been a proposal to set the opening threshold by an adjustable vacuum or by an electromagnet replacing the vacuum.